Publications

NASCENTechnology Publications

Planar LTCC Transformers for High-Voltage Flyback Converters
   Alexander W. Roesler, Member, IEEE, Joshua M. Schare, S. Jill Glass, Kevin G. Ewsuk,
   George Slama, David Abel and Daryl Schofield
   IEEE Transactions on Components and Packaging Technologies, Vol 33 No 2, June 2010
This paper discusses the design and use of low temperature (850 ° to 950 °C) co-fired ceramic (LTCC) planar magnetic flyback transformers for applications that require conversion of a low-voltage to high-voltage (>100-V) with significant volumetric constraints. Measured performance and modeling results for multiple designs show that the LTCC flyback transformer design and construction imposes serious limitations on the achievable coupling, and significantly impacts the transformer performance and output voltage. This paper discusses the impact of various design factors that can provide improved performance by increasing transformer coupling and output voltage. The experiments performed on prototype units demonstrate LTCC transfomer designs capable of greater than 2-kV output. Finally, the paper investigates the effect of the LTCC microstructure on transformer insulation. Although this paper focuses on generating voltages in the kV range, the experimental characterization and discussion presented in this paper applies to designs requiring lower voltage.

Integrated Power Electronics Using a Ferrite Based Low-Temperature Co-Fired Ceramic Materials System
   Alex Roesler, Josh Schare and Chat Hettler, Sandia National Laboratories, Albuquerque, NM
   David Abel, George Slama and Daryl Schofield, NASCENTechnology, Watertown, SD
   2010 Electronic Components and Technology Conference
This paper discusses a new approach to making hybrid power electronic circuits by combining a low-temperature (850 °C - 950 °C) co-fired ceramic (LTCC) substrate, planar LTCC ferrite transformers/inductors and integrated passive components into a multilayer monolithic package using a ferrite-based LTCC material system. A ferrite tape functions as the base material for this LTCC system. The material system includes physically and chemically compatible dielectric paste, dielectric tape and conductor materials which can be co-fired with the base ferrite LTCC tape to create sintered devices with excellent magnetic coupling, high permeability (~400), high resistivity (> 10¹²Ω•cm) and good saturation (~0.3 T). The co-fired ferrite and dielectric materials can be used as a substrate for attaching or housing semiconductor components and other discrete devices that are part of the power electronics system. Furthermore, the ability to co-fire the ferrite with dielectric and conductor materials allows for the incorporation of embedded passives in the multilayer structure to create hybrid power electronic circuits. Overall this thick film material set offers a unique approach to making hybrid power electronics and could potentially allow a size reduction for many commerical dc-dc converter and other power electronic circuits.

LTCC white paper
Low Profile Transformers Using Low Temperature Co-Fire Magnetic Tape
   J Bielawski and George Slama, Midcom Inc.
   A.H. Feingold, C.Y.D. Huang, M. R. Heinz, and R. L. Wahlers, Electro Science Laboratories
There is a growing need for transformers that are low-cost, small, low-profile, and surface-mountable. In addition, they must meet safety requirements while maintaining transformer efficiency. This paper discusses an approach geared to meet these requirements. It involves parallel LTCC processing of ferrite tape and low temperature (850-950 ° C) co-firing of the screen printed silver primary and secondary coils resulting in a small, low-profile, highly reliable product.

Low-Temp Co-Fired Magnetic Tape Yields High Benefits
   George Slama, Midcom Inc.
This article--originally published in the Jan. 1, 2003 issue of Power Electronics Technology, was written by George Slama, who is now part of the NASCENTechnology team. According to Slama, low-temperature co-fired ceramic (LTCC) ferrite, combined with screen-printable silver conductor and low-permeability dielectric produce small, low power, low profile transformers with no wire or discrete core.

Extracting Transformer Parameters
   Steven M. Sandler, CTO, AEi Systems, LLC
   Danny Chow, Engineering Scientist, AEi Systems, LLC
It is often the case, in circuits which use a transformer, that the performance of the circuit is significantly dependent on the characteristics of the transformer. This is true not only in power circuits, but in the case of RF circuits as well. For example, a multi-output flyback power supply uses a coupled inductor as the "transformer." In this topology, the regulation, ripple, stability, and component stresses are all related to the magnitude, as well as the location of, the various leakage inductance terms, as well as, the mutal inductance of the transformer. This is a well known documented concern; however, many transformer datasheets and specifications include only a single measurement for leakage and winding inductance.